The present invention generally relates to methods and systems for identifying “at risk” die on a reticle, and more specifically relates to a method and system for selectively identifying “at risk” die based on location within the reticle which can be used for a multitude of applications including reliability improvement, and through die trace capabilities, for final test disposition and quality control at the customer side.
Patterns corresponding to complex circuitry are formed on a wafer using photolithography. This involves first generating a reticle which is a transparent silica (quartz) plate containing the pattern. Opaque regions on the plate are formed of an ultraviolet light-absorbing layer, such as iron oxide. The pattern is usually created by an electron beam which is controlled by a computer running pattern generation software. Once the pattern is created using the electron beam, the pattern on the reticle is developed in a chemical solution. Once the reticle is formed, it can be used repeatedly to pattern silicon wafers. To make a typical integrated circuit, more than a dozen reticles are typically required, corresponding to different process steps.
It is not uncommon for certain locations on a reticle to be defective, i.e. print repeated defects. In such case, the defect may not always result in a failing die. However, the passing die in that reticle location will be at risk of failing in the field (such as where there is partial bridging on a passing die, in which case the die will be at risk of failing in the field due to heating, shock, etc.). Hence, good die in “at risk” reticle locations are likely to be reliability risks.
As shown in FIG. 1, generally current practice in the industry provides that when an “at risk” pattern is identified during engineering review, the lots are put on hold, and the wafer maps are altered manually. This method may be called “Manual Repeater Downgrading” due to the fact that the method requires manual intervention for identification and rectification. Problems with the method include the fact that it is a manual process, and the fact that there is a risk of overlooking potential problems.